Sandmeyertype

Sandmeyer-type reactions are a family of transformations in which arenediazonium salts undergo substitution by copper(I) reagents with a range of nucleophiles to give diverse aryl products. Named after Traugott Sandmeyer, who reported the original aryl chloride formation from diazonium salts in the 19th century, these reactions form a cornerstone of diazonium chemistry. In the typical sequence, an arenediazonium salt is formed in situ from a primary aromatic amine via nitrous acid, then treated with a copper(I) salt to replace the diazo group with a substituent.

Common variants use copper(I) halides to install halogens: CuCl gives aryl chlorides, CuBr gives aryl bromides, and CuI gives aryl iodides. Other copper salts enable different nucleophiles: CuCN furnishes aryl nitriles, CuSCN yields aryl thiocyanates, and related reagents can introduce additional functional groups. Under certain conditions, hydrolysis with water leads to phenols, a hydrolysis pathway sometimes described within the Sandmeyer-type framework.

Mechanistically, the reaction is thought to proceed via single-electron transfer from copper to the diazonium salt, generating an aryl radical or aryl–copper intermediate that undergoes substitution to form the aryl product and a copper byproduct. The scope encompasses a broad range of substituted arenes, though highly deactivated rings or sensitive substituents can pose challenges, and diazonium salts may undergo side reactions such as hydrolysis, dediazotization, or homocoupling.

The Sandmeyer-type approach remains a versatile tool for introducing halogens, nitriles, phenols, and related functionalities, providing a practical route for preparing aryl derivatives and for enabling further cross-coupling and functionalization in organic synthesis.